This application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to Japanese Application No. 2000-353200 filed on Nov. 20, 2000, the entire content of which is incorporated herein by reference.
1. Field of the Invention
The present invention generally relates to a hydraulic brake device. More particularly, the present invention pertains to a hydraulic brake device for a vehicle having a brake booster.
2. Background of the Invention
A known hydraulic brake device is disclosed in U.S. Pat. No. 3,559,406. This known hydraulic brake device includes a larger diameter piston and a smaller diameter piston. The larger diameter piston is moved by a power piston of a vacuum brake booster that is boosted by vacuum pressure generated by an engine when a brake pedal is operated. The smaller diameter piston is positioned in an inner periphery of the larger diameter piston and is movable relative to the larger diameter piston when the boosting function of the vacuum brake booster fails.
With the construction of the aforementioned hydraulic brake device, when the boosting function of the vacuum brake booster fails, an appropriate braking force can be ensured because the brake pressure can be obtained by the smaller diameter piston and the pressure increase gradient thereof can be greater than the brake pressure obtained by the larger diameter piston. However, the braking force cannot be increased after the brake booster reaches the boosting limit.
A need thus exists for a hydraulic brake device which enables an accurate increase in the braking force after reaching the boosting limit of the brake booster.
In light of the foregoing, the present invention provides a hydraulic brake device which includes a cylinder, a master piston movable in the cylinder in response to operation of an output member of a brake booster in accordance with operation of a brake operation member, a floating piston having a smaller diameter than the master piston and being engaged with the master piston and movable relative to the master piston, a master pressure chamber defined by the cylinder, the master piston and the floating piston, a brake pressure chamber defined by the cylinder and the floating piston, and a valve disposed in the master piston for establishing and interrupting communication between the master pressure chamber and a reservoir tank. A valve actuating member is movable relative to the output member for opening the valve when the valve actuating member is moved by a predetermined amount relative to the output member in accordance with operation of the brake operation member, and a moving amount controlling mechanism reduces the relative movement of the valve actuating member with respect to the output member in accordance with an increase of the operation force by the brake operating member.
According to another aspect of the invention, a hydraulic brake device includes a vacuum booster which boosts an operation force applied to a brake operation member and has an output member and a deformable reaction disk mounted in the output member, a cylinder, a master piston movable in the cylinder in response to operation of the output member of the vacuum booster, and a floating piston positioned in the cylinder and engaged with the master piston, with the floating piston having a diameter that is smaller than the diameter of the master piston and being movable relative to the master piston. A master pressure chamber is defined by the cylinder, the master piston and the floating piston, and a brake pressure chamber is defined by the cylinder and the floating piston. A valve is disposed in the master piston and is adapted to be open to permit communication between the master pressure chamber and a reservoir tank and is adapted to be closed to prevent communication between the master pressure chamber and the reservoir tank. A projecting pin is movable relative to the output member in accordance with operation of the brake operation member to open the valve when the valve projecting pin is moved by a predetermined amount relative to the output member in accordance with operation of the brake operation member. A space provided between the output member and an outer periphery of the reaction disk receives a portion of the reaction disk when the reaction disk is deformed during increased operation force by the brake operating member to reduce movement of the projecting pin relative to the output member.